A 27 kd protein of E. coli promotes antitermination of replication in vitro at a sequence-specific replication terminus.

We have discovered a 27 kd protein of E. coli that binds to a terminator site (tau)-terminator protein (ter) complex and abrogates the replication fork-arresting activity of ter protein in vitro. The 27 kd protein also neutralizes the contrahelicase activity of ter protein, allowing dnaB helicase to unwind DNA past a tau-ter complex. The stimulatory activity of low levels of ter protein on helicase II is also abolished by the 27 kd protein. The binding of the 27 kd protein to a tau-ter complex does not appear to dissociate the ter protein from the DNA. Although the in vivo function of the 27 kd protein is unknown at this time, it has the major attributes of a novel replication antiterminator in vitro.